How does one get Narendra Modi, the front-runner in the race for India’s prime minister, to sit down for an interview?

According to Andy Marino, the British author of a recent biography of Mr. Modi, the answer is simple: “Just call him,” he said by telephone from London.

When a skeptical reporter asked a few times whether it was that easy, Mr. Marino, the only foreigner known to have unfettered access to Mr. Modi, seemed surprised. “Call Modi,” he said. “He is a very personable, open guy. Modi has given his number to ordinary voters, and they’ve called, and they’ve been put through. Or he has called back in an hour.”

Mr. Marino, 49, spent two weeks in August with the Bharatiya Janata Party leader in Gujarat for the book “Narendra Modi: A Political Biography,” which portrays the Gujarat chief minister as a visionary who has been misrepresented by the news media.

Mr. Modi has been accused by many journalists and human rights activists of avoiding tough questions or refusing to take responsibility for his handling of the 2002 Gujarat riots, in which over 1,000 people died, most of them Muslims.

He has been cleared of any wrongdoing by a Supreme Court-monitored investigation, although others have been found guilty of killing Muslims, including a former state education minister. In interviews with the local news media this election season, Mr. Modi has reiterated that he did everything he could to stop the religious violence.

Mr. Marino said that the opposition leader had very likely opened up to him because he was a biographer, not a journalist.

“I think the difference was that I was not being hostile, because I’m a foreigner and not involved — perhaps he felt it easier to talk to me,” Mr. Marino said. “I wasn’t interested in saying, ‘And what did you do then?’ and ‘Why did this happen?’ I was more interested to draw out his background, his thoughts, how he developed and how that fitted into his vision of what India could become. As a result, I was talking about things that he was interested in.”

Mr. Marino said that Mr. Modi had initially caught his attention as someone who could reinvent India’s economy. “People were calling him the Indian Margaret Thatcher in the sense that he would take India away from its Nehruvian socialism. And I wanted to see if that was true,” he said.

Mr. Marino has written two other biographies: “A Quiet American,” about the journalist Varian Fry, who rescued Europe’s intelligentsia during the Second World War, which Kirkus Reviews called a “dramatic story, well told”; and “Herschel: The Boy Who Started World War Two,” which Kirkus Reviews said was “an engagingly written, if often speculative and flawed, biography” of a Jewish boy who shot a German diplomat.

Through the Biographer’s Club in London, Mr. Marino came to know Minhaz Merchant, who had written a biography of the late Prime Minister Rajiv Gandhi. Mr. Merchant, who had contacted Mr. Modi two years earlier when he invited the politician to speak at the Mumbai Press Club, gave Mr. Marino the number of Jagdish Thakkar, Mr. Modi’s public relations officer.

Mr. Merchant later suggested Mr. Marino’s manuscript to HarperCollins India. V. K. Karthika, chief editor at HarperCollins India, said that Mr. Marino’s neutrality and unprecedented access were key considerations in publishing the book on Mr. Modi. “If he could be the next leader of this country, then it’s an important point of view to add to the mix,” she said.

Mr. Marino said that once he called up Mr. Modi’s office, he was able to set up an interview quickly. Mr. Modi did not declare any subjects off limits, including what happened after a train full of Hindu pilgrims caught fire in Godhra after being attacked by a Muslim mob on Feb. 27, 2002, Mr. Marino said.

“By the time we got to the riots, it just arose naturally, and there was no pause at all. He was happy to talk about it in as much detail as I wanted and to whatever length I wanted,” he said.

The chapter on the 2002 riots reads as a record of Mr. Modi’s thoughts and actions during the worst three days of the riots, some of these being shared for the first time. Mr. Marino makes the case that Mr. Modi did everything possible to suppress the religious violence quickly, but the biographer also does not question Mr. Modi’s account of his efforts to stop the violence.

“As the first sketchy reports of deaths came in, the awful truth of the situation began to dawn on Modi. Where were the police?” Mr. Marino wrote. “The fact was he had inherited a state thoroughly marinated in decades of bitter communalism and was left with the consequences of this hate-filled history — a bigotry that had infiltrated the political, bureaucratic and police structure at every level.”

Mr. Marino’s book said letters were sent to the Congress party chief ministers of Maharashtra, Rajasthan and Madhya Pradesh between Feb. 28 and March 1, but only Maharashtra responded with a limited number of personnel.

Mr. Modi told Mr. Marino, “I feel sad about what happened, but no guilt. And no court has even come close to establishing it.”

Though Mr. Marino insisted that a simple request was enough to get access to Mr. Modi, others have found it much more difficult to get Mr. Modi to talk freely.

Sandra Petersmann, South Asia correspondent at ARD German Public Radio, said that her news outlet had been trying to get an interview with Mr. Modi for over one year because its listeners in Germany were curious to hear from the man who could be the next leader of the world’s largest democracy.

Ms. Petersmann said that she wasn’t interested in judging Mr. Modi but that she wanted to ask him why he had not candidly taken responsibility for the violence in 2002. “I come from a country with a history of violence, and we know that it is important to keep questioning,” she said.

Nilanjan Mukhopadhyay, an Indian journalist who was granted access to Mr. Modi for his book “Narendra Modi: The Man, The Times,” which came out last year, said the 2002 riots had been off limits during their discussions. Instead, Mr. Modi told him to read his testimony in the investigation. “And I was careful not to cross that line,” he said.

So far, Mr. Marino’s biography has received little attention in India. One book review published on Saturday on the website of the cable TV channel CNN-IBN said, “Marino’s book is indeed no hagiography; neither is it coldly objective. It warms up to Modi but is not dazzled by him, thereby leaving the aftertaste of having read about someone who is more ‘hero’ than ‘villain.’ ”

But Ms. Karthika of HarperCollins India said that Mr. Marino’s book was being reprinted soon after the first run of 5,000 copies sold out.

Mr. Marino said he had not received any feedback from Mr. Modi about the book, but he was satisfied that he had fairly portrayed a leader he said had been vilified by the news media. If Mr. Modi becomes prime minister, his critics will come to see Mr. Marino’s point of view, the author said.

“They’ll find out that things will get better, then they won’t hate him so much,” he said. “Kind of like Thatcher. She did a lot of good, but she is still virulently hated by sections of the population — but interestingly enough, less than it used to be.”

Betwa Sharma is a freelance journalist based in New Delhi. Follow her on Twitter @betwasharma.